In conventional cellular communication networks, a fixed base station (BS) is responsible for controlling communications with the mobile stations (MSs) within the coverage area of that BS. The BS maintains control by selecting channels and communicating directly with the MSs. Thus, conventional cellular communication networks are considered single hop networks.
The limitations of single hop cellular networks are known. For example, the coverage of single hop cellular networks is limited by radio “dead spots” caused by interference from structures (e.g., buildings, etc.) located in the paths of the radiated signals. Also, the coverage of these networks is limited by the transmit power of the MSs. Significant increases in MS transmit power in single hop cellular networks increases signal interference, which decreases network capacity and throughput as a result.
Additionally, in code division multiple access (CDMA) single hop cellular networks, other limitations are known. For example, in single hop cellular networks operated in accordance with the IS-95 or CDMA2000 standards, each MS can be connected to multiple BSs simultaneously. Consequently, in CDMA single hop cellular networks, so-called “soft handoffs” occur whereby multiple BSs (and/or sectors) maintain their connections with an MS until after a handoff is completed. Thus, soft handoffs are described as “make before break” handoffs.
In the reverse links of conventional CDMA single hop cellular networks, each MS is required to set up the respective connections with the multiple BSs and/or sectors involved. Consequently, in order to perform soft handoffs in CDMA single hop cellular networks, a substantial amount of processing complexity is built into each MS, which significantly increases the technical complexity and expense of each mobile handset or device used.
In order to resolve the problems encountered with conventional signal hop cellular networks, standards that support multi-hop cellular communications have been approved. For example, IEEE Standard 802.16-2004 (formerly known as IEEE Standard 802.16d) for local and metropolitan area networks specifies the air interface for fixed broadband wireless access (BWA) systems supporting multimedia services. The medium access control (MAC) layer specified in Standard 802.16-2004 supports the use of point-to-multipoint architectures and mesh topologies. Using a mesh topology, a source node in a mesh network can communicate with a destination node via one or more intermediate nodes, and network control is distributed or decentralized. Thus, in the context of a cellular network using a mesh topology, a BS in a multi-hop cellular network can communicate with an MS via one or more fixed or mobile (intermediate) relay stations.
The advantages of multi-hop cellular networks over single hop cellular networks are known. For example, in multi-hop cellular networks, a BS can communicate indirectly with an MS via an intermediate relay station. Consequently, by providing alternate propagation paths, the effects of radio “dead spots” in these networks can be reduced. Also, because intermediate mobile or fixed relay stations can be used in multi-hop cellular networks, the transmit power of the individual MSs in these networks can be reduced. As a result, signal interference in multi-hop cellular networks can be reduced, which increases network capacity and throughput.
Although standards and protocols have been approved that support the use of multi-hop cellular communication networks, a number of important technical problems need to be resolved before such networks can be implemented. For example, in order to implement a multi-hop cellular network successfully, suitable bandwidth allocation mechanisms have to be developed with distributed access and control network objectives in mind. Also, suitable soft handoff mechanisms have to be developed for CDMA multi-hop cellular networks, which will reduce the technical complexity and expense of the mobile cellular communication devices involved.